Production of furfural



Patented Apr. 27, 1937 UNITED. STATES PRODUCTION OF FURFURAL Ellis I. Fulmer, Leo M. Christensen, and Ralph M. Hixon, Ames, Iowa, assignors to The Chemical Foundation, Incorporated, a corporation of Delaware No Drawing. Application December 14, 1935,

Serial No. 54,374

1'! Claims.

It has long been known that pentoses such as xylose, pentosans such as xylan, and pentosancontaining materials such as cereal straws and husks, corn-cobs and wood, yield furfural when 5 heated with dilute mineral acids. At the present time Iurfural is commercially manufactured from oat hulls by a process involving acidification with sulfuric acid, steam distillation and subsequent separation of the furfural and water by fractional l distillation and decantation.

Furfural is rapidly polymerized under the conditions which bring about its formation, with the result that present commercial yields are only about 50 per cent. of that theoretically obtainable.

15 Furthermore, the isolation of the furfural from the distillate is a tedious and expensive procedure.

It is the object of this invention to provide an improved alternative procedure which will be free to a great extent from the above difiiculties and 20 which will, therefore, while affording an increased yield, also effect a saving in time, labor and cost, and thereby permit a lower price for furfural, making it possible to expand the market for this product as obtained from farm wastes. Our process differs from that at present used chiefly in the manner by which the furfural is removed from the reaction medium and the chief advantage of our process results from the more rapid removal thus obtained, so that less of the 30 furiural formed undergoes polymerization and loss. In addition, however, our process yields fur- ,fural in a solution from which it may be recovered by simple fractional distillation, thus appreciably lowering the processing cost. Prior processes re- 35 quire and involve an antecedent steam distillation. Furthermore, the acid concentrations used in our process are much lower than those used in the prior art and thus further reductions in the cost of processing are obtained.

, 40 In our process, dehydration and condensation of the pentose or pentose-yielding substance to produce furfural is conducted in an aqueous medium containing a suitable concentration of acid and salt, the salt functioning to increase the 45 activity of the acid and to decrease the solubility of furfural. We remove the furfural from the reaction medium by. means of a solvent which is relatively immiscible with water but in which furfural is soluble, and extract the liquid in the aqueous phase. In this manner we have obtained yields of furfural of as much as 80 per cent. of theoretical as compared with the 50 per cent. obtained by present methods.

In our process, we may employ directly such materials as oat-hulls, corn-cobs, cereal straws, cotton seed hull bran, wood, or similar materials, or we may first prepare the pentose, such as xylose, or the pento'san, such as xylan, from such materials by methods already known to those on skilled in the art, and use these materials, either in dry form or in solution, in our process. We may use various salt-acidcombinations and may employ any of a number of extracting agents. The salt-acid mixture must, however, give a reaction more acid than about pH 1.0 and the solvent must be of convenient .boiling point, be

relatively immiscible in water and in the reaction medium, .be a good solvent for furfural, and further must not itself react with the other materials employed.

The furfural-yielding material is placed in a suitable vessel with the acid and salt. This mixture is heated to the proper temperature and continuously extracted with the furfural solvent. The iurfural is thus removed and may be concentrated in the receiving vessel by distilling ofl the solvent, when it is the lower boiling constitutent, the solvent being used to extract additional furfural from the reaction medium. If the solventfurfural extract is appreciably acid, it is usually desirable to add a neutralizing agent, such as calcium carbonate, to the receiver. The furfural is then recovered in pure form by fractional distillation of the solvent-furfural mixture.

It is obvious that acid concentration, salt concentration, temperature and time of heating are factors of the greatest importance. each combination of acid and salt, there is some minimum time of heating and extractingat the temperature selected. This is clearly shown by the data in the following table, which gives the results obtained when a solution containing 20 grams of xylose per 100 cc., saturated with sodium chloride and containing the indicated amount of hydrogen chloride, was extracted with toluene at 105 C. The best yields of furfural and the time of heating required are shown.

Time 01 a s??? lurinral yield ex g g gg to give ilnoograms p? maximum grams, i'urfurahyield xylose added in hours 0. 25 35 13 0. 60 38 10 o. 7a 41 7 1. 00 40 l. 60 '39 3 2. O0 37 2 Thus, for

a mixture of'hydrofluoric acid with sulfuric acid affords an acidity equally that of a superconcentrated-hydrochloric acid. In general, lowering the reaction temperature increases the time and/or 5 acid concentration required, and we prefer to operate near the boiling point of water at the pressure employed. We may use lower salt. concentrations but this also increases thetime of reaction and/or acid concentration n'ecessaryand generally has given lower yields than those obtained with greater salt concentrations. I We therefore prefer to employ suificient salt to produce a solution saturated at the reaction temperature.

The following are examples of the way in which we operate our process, but we do not limit ourselves to these examples. Thus, we may employ other solvents than toluene, other acids than hydrochloric, or other salts than sodium chloride,

or other pressures than atmospheric, without departing from the scope of this invention.

Example 1 flask was then heated to 105 C. and the extraction continued, the furfural-toluene mixture returning to the receiver. After five hours of extraction, during which the temperature of the reaction was held at 105 C., the ifurfural-toluene mixture was removed from the receiver and from the reaction vessel and the furfural recovered by fractional distillation, the yield being 18 parts by weight of the oat hulls used. The theoretical yield of furfural, as measured by the standard analytical procedure, was 21.5 per cent. Thus the yield by our process was 83.5 per cent. of the theoretical. e

The expression water immiscible solvent, and similar expressions used in the applicants. claims, is'intended to define a solvent which has a decided and preferential afflnity for the furfural gree. The essence of the invention is to remove 60 furfural as formed, from an aqueous phase, and

largely absorb it in a solvent phase, which solvent phase is, substantially non-aqueous, so that the furfural is thereby protected from polymerization'". other reactions which wouldbccur in aqueous phase mder the conditions 0.1 the eatment3 WWW. this-example, 120 parts of a solution containing 19 parts of *xylose were used. To this.

*were added 45 partsof sodium chlorideand suf-.

' flcient hydrochloric acid to give a normality of 1 0.50. was heated to 105 C. and extracted with toluene as before for five hours. The yield of furfural was 9.1 partsby weight. The theo- 75 retical yield is 63.4 per cent. by weight, or 12 9 parts by weight from the 20 parts of xylose used in this sample. The actual yield was, therefore, 70 per cent. of the theoretical.

Having thus described our invention, we claim as new: 5

1. The process of producing furfural consisting in reacting a furfural-yielding material with a suitable acid, in an aqueous medium, simultaneously extracting the reaction product with a liquid solvent of furfural which is immiscible with 10 water, and fractionally distilling the resulting so.- lution.

2. The process of producing furfural consisting of reacting a furfural-yielding material with a suitable acid in an aqueous medium, in the 15 presence of a salt adapted to decrease the solubility of furfural, and simultaneouslyextracting the reaction product with a liquid solvent of furof said acid, and simultaneously extracting the furfural solvent which is immiscible in water, and

mixing with said acid a second acid adapted to raise the acidity of the mixture above that of 40 either component acid.

6. The process of removing furfural' as formed by the reaction of afurfural-yielding material with an acidulating agent in an aqueous medium, which consists in preventing thepolymerization 45 of the furfural by extracting the reaction product as formed with a liquid furfural solvent which ,is-relatively immiscible with water; and Iran-- tionally distilling the solution.

7. The process'ofremoving furfural, formed 50 by the reaction of a furfural-yielding material with an acidulatingagent in anaqueous medium, which comprises, extracting the reaction product as formed with a substantially water immiscible, liquid furfural solvent, in the presence of a salt adapted to increase the activity of the acid andto decrease the solubility of furi'ural. and recovering the furfural fromthe furfural solution by fractional distillation.

8. The process for the-production and isolation of furfural comprising effecting a reaction, in an aqueous medium, between furfural-yielding materials and a suitable acidulating agent, in the presence of a water immiscible, liquid solvent of 'furfural, removing the furfural solvent mixture consisting in effecting a reaction, in an aqueous medium, between furfural-yielding materials and a suitable acid, in the presenceof a water immiscible, liquid solvent of furfuP-al, removing the furfural solvent mixture and separating the solvent therefrom for reuse in the reaction.

I 10. The process for the production and 18018- tion of furi'ural consisting in effecting a reaction, in an aqueous medium, between furfural-yielding materials and a suitable acid and in the presence of a liquid, water immiscible furfural solvent, removing the solvent mixture from the reaction zone, separating the solvent from the mixture and recycling the solvent to the reaction zone.

11. A process for the production and isolation of furfural consisting in effecting a reaction between furfural-yielding materials and an acidulated aqueous medium, said medium containing a suitable concentraction of an acid and salt adapted to decrease the solubility of the furfural, simultaneously extracting the furfural with an excess of a liquid. water'immiscible furfural solvent, and subjecting the furfural solution to fractional distillation.

12. The process of isolating furfural as formed by the reaction of a furfural-yielding material with an acidified aqueous medium comprising effecting said reaction, in the presence of toluene, and subjecting the resulting toluene solution of furfural to fractional distillation.

13. The process of isolating furfural as formed '25 by the reaction of a furfural-yielding material with acidified aqueous medium comprising effecting the reaction in the presence of toluene to extract the iurfural as formed, withdrawing the toluene solution of furfural from the reaction 30 zone, separating the toluene from the solution and returning the toluene to the reaction zone.

14. The process of isolating furfural as formed by the reaction of a furfural-yielding material with an aqueous medium acidified with hydrochloric acid, consisting in extracting the reaction product as formed with toluene, removing the resulting toluene solution of i'urfural from the reaction zone, subjecting the solution to fractional distillation and recycling toluene to the reaction zone.

15. The process of isolating furfurai as formed by the reaction of a furfural-yielding material with an aqueous hydrochloric acid solution comprising extracting the reaction product as formed with toluene, removing and neutralizing the solvent extract and subjecting the toluene solution of furfural to fractional distillation.

16. The process of isolating furfural as formed by the reaction of a furfural yielding material with an acidified aqueous medium comprising eifecting the reaction in the presence or benzol to extract the furfural as formed in the benzol solution, removing the benzol solution of Iuriural and subjecting such solution to fractional distillation.

17. The process of isolating furfural as formed by the reaction of a furfural-yielding material with an acidified aqueous medium comprising effecting such reaction in the presence of benzol to extract the furfural as formed, removing the benzol solution of furfural from the reaction zone, separating the benzol therefrom and returning the benzol for reuse in the extraction.

ELLIS I. FULMER. LEO M. CHRISTENSEN. RALPH M. HIXON. 

